Pressure control in a hydraulic circuit is carried out using valves. Known in this respect is the use of safety valves, or relief valves, in order to maintain a constant pressure in the hydraulic circuit and thereby prevent pressure peaks which could harm the various parts of said circuit. These pressure peaks, which can give rise to the phenomenon of water hammer, must therefore be controlled effectively.
Conventional safety valves, used mainly in hydraulic circuits, essentially comprise a body provided with an inlet and an outlet, a closing element or gate which is mounted hinged to the valve body and which divides the aforesaid inlet and outlet, a seat formed in said body and against which said gate rests, hinge means of the gate on the valve body, and means for keeping the gate in position against the seat. One of the main disadvantages presented by this type of valve, and more specifically the valves known as "clapet" valves, is that when a large volume of fluid has to be evacuated the means to keep the gate in position can generate considerable pressure variations which are a function of the movement of the gate, which in turn depends on the different quantities of fluid to be evacuated.
The disadvantages are considerably greater when this type of valve is used in pneumatic circuits. This is the case due to the fact that the effect of water hammer is more critical. The flow of air in a pneumatic circuit causes the gate to undergo an oscillatory movement which is harmful to it. Indeed, it has been found in practice that the gates of these valves fail by breakage of their hinge pin due to fatigue. Gate failure is extremely important from a technical point of view and from a financial point of view. In installations which work with a pneumatic circuit with large air flows, as, for example, the circuits for sewage water treatment plants or vacuum installations, operation of the installations must be stopped every 2 or 3 months in order to replace the valves. This has a negative effect on the cost of maintenance of the installation and means that a schedule of operation of the installation must be drawn up in function of the maintenance stops that have to be carried out ever so often.
It must further be taken into account that the problems deriving from failure of conventional safety valves can, for example, cause a pneumatic valve to turn in opposite direction due to overpressure in the system, thereby causing breakdown of that system.
The prior art comprises valves with a structural arrangement designed to reduce the cited oscillatory movement of the gate and, therefore, what is called the "flag effect". Some solutions have been proposed in this respect in an attempt to reduce said effect, although such configurations result in a design that is too expensive for the installation.